I'll add my two cents here and say that I would slightly disagree and recommend a four-night trip as your first. I think three nights is just too short and that the temptation could be to try to cram "doing everything" into a three night voyage, which would make the whole trip feel VERY rushed, hectic, etc. Consider that even with an early boarding group you won't be on the ship before 11:30 or 12, plus the mandatory safety drill, and really you're only getting half a day max on the ship the first night. Four nights gives you a little extra time without committing you to a full week if someone has motion sickness, has anxiety about being in open water, etc. That being said, my first two
DCL sailings were 7 Night cruises, one with three kids and the other with four. Both were amazing! We've been hooked ever since.
As far as which port to use, if every other consideration is equal (flights, pre-night hotels, transfers, etc) I recommend Port Canaveral or San Diego. While San Diego is completely void of the "Disney touches" that are everywhere in PC, I can't say enough for how much we enjoyed our embarkation experience there. We stayed at a reasonably priced hotel across the street from the port, woke up with a view of the Wonder, literally WALKED across the street to the terminal when it was our time to board, breezed through security and were sitting having lunch in Cabanas less than a full hour after we left the hotel room. After the cruise, the airport is a 10 minute uber ride from the cruise terminal. Since you're traveling with small kids, this easy "in and out" experience is, in my opinion, hugely underrated.
While getting to and from PC from the Orlando International Airport is a bit more labor intensive (and expensive), the cast members at PC and the overall terminal experience are beyond excellent, particularly if you're traveling during any of the "Special Sailing" periods like Halloween on the High Seas or Very Merrytime sailings. It's still my favorite port, but San Diego was great, too. Vancouver was mostly ok, but I feel like we did a LOT of walking between checking in at the terminal and actually boarding the ship. We had a stroller and various other items that made the walk feel longer than it probably was, but it wasn't my favorite boarding experience overall. I REALLY didn't like New Orleans. We haven't used Galveston yet (which is wild since we live in Texas) but I think most people have decent experiences there.
That's probably way more info than you were looking for, but I hope it helps!
No matter which port you use and how many nights you sail for, I'm sure you're going to have the best time.
